Django provides a really good model for allowing users to customize the
behavior of Class Based Views. It's in line w/ what Daniel/Kaxil and co are
saying about a consistent backend class. It uses a standard base class as
well as a default concrete implementation. Customization then only requires
setting an explicit class if you're overriding the default.
Seems that the interface is more important than the backend mechanism to
make this work. There are multiple ways to make this work internally, but
the interface should be in line with future plans for hooks/extensible
areas.
Just to make things concrete, here's my understanding of what that would
look like / what they're suggesting.
*BaseTimetable abstract class*
- Defines a `*get_next_execution_time*` method. This method accepts
one argument, an arbitrary datetime value. Based on that datetime, this
method returns the next time the DAG should start. This makes it easy to
schedule past events, and also makes it easy to print out a "dry run" of
execution times for testing purposes.
- Defines a *'_check_timetable_arguments*` method that looks for any
existing timetable args in the DAG and makes sure they're used by whatever
Timetable class is selected. Error checking.
*CronTimetable* - Default TimetableClass. Built on BaseTimetable.
If they want a different timetable, they can just extend BaseTimetable and
define a custom `get_next_execution_time` class. Then pass the class into
the DAG constructor under the `timetable_class` argument. So for `sunset`
or `sunrise`, they could easily create a `SolarTimetable` class and pass
that in.
`get_next_execution_time` can then be called whenever DAGs are parsed or
whenever tasks run.
On Wed, Jan 20, 2021 at 3:53 PM James Coder <jcode...@gmail.com> wrote:
> Kaxil you beat me to it. I actually have a dag where I achieve an
> irregular schedule by overriding DAG.next_dagrun_info(). If that method
> were swapped out for an object it may be a semi-easy way to make the
> schedule “plugable”.
>
> James Coder
>
> On Jan 20, 2021, at 6:37 PM, Kaxil Naik <kaxiln...@gmail.com> wrote:
>
>
> "CronBackend" / "ScheduleIntervalBackend" :D similar to Xcom and Secrets
> Backend
>
> Would be definitely good to have Custom Schedule intervals using
> functions/class that is Serializable too.
>
>
> On Wed, Jan 20, 2021 at 11:02 PM QP Hou <q...@scribd.com.invalid> wrote:
>
>> On Wed, Jan 20, 2021 at 10:22 AM Daniel Imberman
>> <daniel.imber...@gmail.com> wrote:
>> >
>> > I love the idea of allowing users to create their own scheduling
>> objects/scheduling python functions. They could either live in the
>> scheduler or as a seperate process that trips some value in the DB when it
>> is “true”. Would be great from a “marketplace” standpoint as well as users
>> could post their custom scheduling objects for others to use.
>> >
>>
>> I like this idea as well, a quick escape patch for custom and complex
>> scheduling behaviors without having to wait for upstream support.
>>
>
